1. Field of the Invention
This invention relates to a method and apparatus for testing a fluid conduit system, such as a domestic fuel gas supply system or installation, for gas leaks and, more particularly, for monitoring and determining the volumetric leakage rate of gas from such a system or installation.
2. Discussion of the Background
The portion of the domestic system with which the applicants are primarily concerned comprises: the pipework between the gas meter and the main stop cock or valve (normally at or fairly close to the upstream, inlet side of the gas meter); the gas meter itself; and the pipework between the outlet of the meter and the gas control valve(s) on the downstream appliance(s). One presently used method for testing such systems for leaks where there is a suspected leak involves isolating the system by closing the stop valve and the or each gas control valve, pressurising the system by opening the stop valve, closing the stop valve, and from a predetermined pressure in the system measuring the pressure drop in the isolated system over a set length of time. If a predetermined maximum acceptable pressure drop is not exceeded then the system is considered to be sound.
The above described present method assumes that all such system portions have approximately the same volume. In the past this was a reasonably valid assumption to make since the volume of the gas meter has by far contributed the major part of the total volume of the isolated system and in the UK a standard domestic gas meter has been employed for many years. Consequently, the volume differences in the pipework in different systems could be ignored. However, with the introduction of new, relatively low volume gas meters it will no longer be appropriate to ignore the differences in the pipework volume from system to system or the differences between different low volume gas meters and thus the assumption previously made will no longer be a valid one.
A method of testing an industrial gas system or installation to determine the volumetric leakage rate without having to ascertain or assume volume of the system being tested is known already. The method involves isolating the system, pressurising the system to a predetermined pressure, measuring the pressure drop (.DELTA.P.sub.1) in the system from that predetermined pressure over a fixed time period (T.sub.1), repressurising the system to the same starting or predetermined pressure and introducing a calibrated orifice, i.e. a known `artificial leak`, into the system, and then measuring the time period (T.sub.2) over which the same pressure drop (.DELTA.P.sub.1) occurs with the system leaking as a result of both the actual leak and the `artificial leak`.
The leak rate of the installation is obtained from the equation: ##EQU1## where F is the known flow rate through the artificial leak measured at the same pressure.
The above described methods are carried out manually employing a so-called `U gauge` manometer to measure the pressure drops and a stop watch to measure the time periods.